The invention relates to an internally-fused capacitor.
An internally-fused capacitor includes one or more fuses within a capacitor housing. The fuses protect capacitor elements from overcurrent conditions that may result in the release of expanding gases that could damage the housing and the capacitor elements. A typical fuse assembly employs a small conductive wire that disintegrates in response to excessive electrical current. The fuse may be confined between kraft paper, or boards, which are inserted between the capacitor elements. Typically, one end of the fuse is soldered to a metal conducting foil edge of a capacitor element and the other end of the fuse is soldered to a metal collector bus.
When a capacitor element fails, the element creates a short circuit through which energy stored in capacitor elements connected in parallel with the failed capacitor element may discharge. The fuse disintegrates in response to the excessive current resulting from this discharge, which breaks the electrical connection between the failed element and the collector bus. With the failed element thus removed from the circuit, the capacitor can continue to operate using the remaining elements until enough elements fail to cause overvoltage or unbalance conditions that exceed set protective levels.
In one general aspect, an internally-fused capacitor includes a capacitor housing, at least one capacitor module, and at least one fuse assembly. The capacitor module is positioned in the housing and includes capacitor elements. Each capacitor element includes a first extended foil edge on a first end and a second extended foil edge on a second end. The fuse assembly is positioned in the housing and includes a fuse wire adjacent to the capacitor element. The fuse wire is connected at a first end of the fuse wire to the first extended foil edge by a crimped connection.
Embodiments may include one or more of the following. For example, the internally-fused capacitor may further include at least one fuse card positioned in the housing and including a base with barriers protruding from the base and defining channels. Fuse assemblies are positioned in the channels.
The crimped connection may include a mechanical crimp between a crimp plate and the fuse wire at the first extended foil edge. The crimp plate has a pair of faces that may be compressed against the first extended foil edge. The crimp plate may include a barrel connector with the fuse wire crimped in the barrel connector.
The fuse wire may be enclosed along a portion of its length in a fuse tube which may serve to help extinguish the arc created by the disintegration of the wire. The fuse tube also may absorb breakdown energy and direct breakdown products away from the capacitor elements.
The internally-fused capacitor may further include a terminal extending from the housing and a terminal wire connected between the terminal and a second extended foil edge of a capacitor element by a crimped connection.
The internally-fused capacitor may further include a second capacitor module and fuse assemblies positioned in the housing. The second capacitor module includes capacitor elements, each of which includes first and second extended foil edges. Each fuse wire is connected at a first end to the first extended foil edge by a crimped connection. The internally-fused capacitor may further include first and second fuse cards, each of which includes a base with barriers protruding from the base and defining channels. Each fuse assembly is disposed within one channel. The internally-fused capacitor may further include a jumper lead connected at a first end to a first fuse wire node of the first capacitor module and at a second end to a second extended foil edge of the second capacitor module.
The internally-fused capacitor may further include a jumper lead connected at a first end to a first fuse wire node of the first capacitor module and at a second end to a second fuse wire node of the second capacitor module. The first fuse wire node includes an electrical connection through fuses to the first extended foil edges of the capacitor elements of the first capacitor module. The second fuse wire node includes an electrical connection through fuses to the second extended foil edges of the capacitor elements of the second capacitor module.
The fuse cards include a dielectric insulating material, such as polypropylene. The fuse tube may be made of an insulating material, such as silicone rubber.
The internally-fused capacitor offers considerable advantages. For example, conventional internally-fused capacitors confine the fuse between dielectric kraft paper separating energized elements. The paper is easily damaged by the mechanical forces created when an element fails. As a consequence, a capacitor element failure may damage a neighboring fuse that protects an adjacent, and functioning, capacitor element. This can result in the premature removal of a sound element. This also can allow energization of a previously-isolated failed element, which can lead to a capacitor failure that ruptures the capacitor housing. Placing the fuses in individual tubes and placing the tubes in channels in a fuse card help to ensure that operation of a fuse will not affect adjacent elements.
The internally-fused capacitor also prevents the generation of excessive gas and residue associated with a fuse disintegrating adjacent to kraft paper, which can contaminate insulating materials and dielectric fluid in the capacitor housing. If the gas and residue are absorbed and redistributed through the remaining sound sections of the capacitor, such as, for example, in the dielectric fluid, the integrity of the remaining elements may be jeopardized.
In particular, using a crimping operation instead of conventional soldering operations protects dielectric materials made from polymers, such as polypropylene, which may be damaged by the heat generated during soldering. Crimping also offers the considerable advantage of providing a joint that may be easily inspected for quality assurance purposes. By providing repeatable, high quality crimp joints, electrical loss through the joints may be reduced, which provides cost savings to the user. In addition, by reducing the electrical loss through the joints, associated resistive heating is reduced to thereby reduce damaging heat effects on the internal structure of the capacitor.
Other features and advantages will be apparent from the following description, including the drawings, and from the claims.